This invention is directed to transferring and fusing a toned image layer from an image receptor to a recording medium, such as paper. Toned image layers are images formed by a finely divided marking material referred to in the imaging art as "toner."
Several known processes are available for forming the toned image layer. For example, in xerography a uniform electrostatic charge is placed on a photoconductive insulating layer in the dark. The electrostatically charged surface is then selectively exposed to a light and shadow image to form a latent image thereon. Examples of electrostatic formation of latent images are disclosed in U.S. Pat. Nos. 4,408,214, 4,365,549, 4,267,556, 4,160,257, and 4,155,093. The resulting latent electrostatic image is developed to provide a visible reproduction of an original by depositing toner on the latent image. Toner is principally attracted to those areas of the photoconductive layer which retain a polarity of charge opposite to the polarity of charge on the toner particles, thereby forming a visible toned image layer corresponding to the electrostatic latent image.
Alternatively, a toned image layer may be formed by an ionographic imaging process. In an ionographic imaging process, a latent image is formed on a dielectric image receptor or electroreceptor by ion deposition, as described, for example, in U.S. Pat. Nos. 3,564,556, 3,611,419, 4,240,084, 4,569,584, 4,408,214, 4,365,549,4,267,556, 4,160,257, and 4,155,093. Generally, the ionographic process entails application of charge in an image pattern with an ionographic writing head to a dielectric receiver that retains the charged image. The image is subsequently developed with a developer capable of developing charge images.
The toned image layer may then undergo further processing and, finally, be transferred to a recording medium, such as paper. The transferred image may then be permanently affixed, or fused, to the recording medium by various conventional fixing methods, such as the application of heat or pressure or use of a solvent.
The toner used for such processes are generally composed of a thermoplastic resin and a colorant, such as a dye or pigment. Examples of suitable resins are disclosed in U.S. Pat. No. 4,476,210, and examples of suitable colorants are disclosed in U.S. Pat. Nos. 4,476,210, 4,464,252, 4,480,021, 4,794,651, 4,762,764, 3,729,419, 3,841,893, and 3,968,044.
Additionally, the toner may be used in combination with a suitable carrier, and additives such as a charge control agent, pigments, a flow improver or the like. Various toner compositions are disclosed in U.S. Pat. Nos. 4,659,640, 4,476,210, 4,794,651, 4,762,764, 3,729,419, 3,841,893, and 3,968,044.
Toners are generally manufactured by a process in which the colorant is uniformly dispersed in the resin by heating and blending the toner ingredients in a suitable mill. After cooling, the blended mixture is then pulverized to form it into finely divided particles within the desired size range.
Toners may be in a dry or liquid form. For example, toner may be in the form of a dry powder, such as is used in xerographic copying. Alternatively, the toner may be in the form of an electrostatic liquid ink wherein the toner particles are dispersed in a liquid carrier, such as is used in electrographic type printers.
Imaging processes may be used to develop black and white, single color, or multi-color images. Multi-color imaging may be done either as a fully formed image or a step formed image. A fully formed image implies that an image with multiple colors is fully formed on the image receptor and then transferred to the recording medium in a single step. In a step formed image the colored toner images are individually formed on the image recorder and transferred to the recording medium one color at a time. Processes for forming monochromatic or polychromatic electrostatic images are disclosed, for example, in U.S. Pat. Nos. 3,672,887, 3,687,661, 4,395,472, 4,353,970, 4,403,848, and 4,286,031.
Previously, methods have been proposed for developing the toned image layer on an image receptor, transferring the toned image layer to a recording medium, and subsequently fusing the toned image layer to a recording medium, such as paper. One such method employs a dry powder type of pressure fixable toner to form the toned image which is transferred from a photoreceptor to a paper recording medium and subsequently affixed thereto by use of a cold roller with high nip pressure. Such pressure-type image transfusion is employed in commercial printers sold by Delphax Co.
Another method for developing, transferring, and fusing a toned image involves a thermal-type system wherein a toner image is formed on a photoreceptor with a thermally fixable toner. The toned image is transferred from the photoreceptor to a paper recording medium and subsequently affixed thereto by the application of heat.
One apparatus for such thermal fixing is disclosed in U.S. Pat. No. 4,435,069, wherein an infrared radiation heat source is used to fix an image. A backing roller transports a recording sheet to a fixing drum having an infrared radiation heat source in its interior. A toner image on the recording sheet is permanently fused to the sheet when contacted with heat permeated from a heat-absorbing area of the drum.
In another example of toner image development, U.S. Pat. No. 4,303,924, discloses a jet drop printing process wherein a radiation curable ink is first jetted onto a recording sheet and then cured by irradiation with, e.g., ultraviolet radiation energy.
There has not been developed, however, a simplified one-step method of simultaneously transferring and fusing (hereinafter referred to the combined step of transferring and fusing as "transfusing") an image from an image receptor to a recording medium.